1. Field of Invention
This invention relates to an optical receiver system, and more particularly to a monopulse optical receiver system for determining the angle of incidence of a single incident light pulse.
2. Description of the Prior Art
Optical radars employing optical receivers or detector circuits for determining the angle of incidence of a reflected, monochromatic light wave are well known in the state of the art. However, these optical receivers require the presence of a continuous incident light beam, or of a continuous series of ligh pulses. One such system is described in a patent to Brunkhorst et al, U.S. Pat. No. 3,800,146 wherein a pulse optical radiation tracker uses a radiation sensitive detector having two pairs of opposed output electrodes mounted in a quadrant to detect an incident light beam or series of incident light pulses and to determine the incident angle of the light beam with respect to the two planes within which the two pairs of electrodes are mounted, the information being provided by the output voltages of the electrodes whose magnitudes are dependent upon the relative location of the incident light spot with respect to the position of the electrodes. Another system for providing incident angle information for a continuous beam of impinging light in an "off axis" tracking system is described in a patent to Webb, U.S. Pat. No. 3,435,246. In the Webb patent the angle of incidence of all impinging light beams which are non-perpendicular to the plane of the optical detecting surface and which deviate from the perpendicular by a determined value are received by the detector through a baffle of two parallel grids which control the amount of incident light impinging upon the surface of a photoelectric sensor in dependence upon the deviation of incident light angle from the perpendicular. As in the hereinbefore mentioned Brunkhorst patent, the system disclosed by Webb also requires a continuous light beam, or a continuous series of light pulses to determine the angle of incidence, which is typical of all of such systems generally disclosed in the art.
The existence of a radiant source producing a continuous coherent source of light permits the use of nulling or scanning devices and systems to make the requisite angle measurement. However, for a situation in which a single light pulse is received, such nulling or scanning devices are inadequate for determining such incident angles. One situation in which single, or monopulse light waves are encountered is that of military warfare employing the use of laser guided bombs. Typically, such laser guided bomb weapons transmit a single pulse of monochromatic light which are non-periodic and which determine the range, and target identification prior to releasing a bomb or firing a missile. The target vehicle exposed to such laser devices is vulnerable and unable to institute countermeasures unless the presence and position of the attacking vehicle is known. Therefore, the target vehicle must determine the angle of incidence of the impinging light beam in order to determine the relative location of the attacking vehicle.